Fuse Keeps Blowing- advice? Options

[mikedsilva]

My new to me, 1970 914/4, has some iffy electrics..

The fuse in the number 7 spot, keeps blowing as soon as I turn the key to ignition on.

So, this means I dont have any indicators or wipers working.. etc.

Electrics are a little mysterious to me to be honest.. I do have a multimeter.. but I am not sure how to track this problem. I'm thinking I have a short somewhere on one of those systems..

Should I start by trying to unplug each and every component that uses that circuit, then reinstall another fuse, and turn the ignition on?

How would an experienced auto electrician pinpoint a problem like this?

Any and all advice appreciated..

Cheers
Mike.

[BeatNavy]

I'm certainly no master electrician either but it definitely sounds like you do have a short. Are you sure it's fuse 7? On the '71 Wiring Diagram it shows that that is only part of the license plate light circuit (through the main light switch).

Here's a link you'll need: Wiring Diagrams. Take your time and study this a little. It's hard to see, so you may have to zoom in with your browser when tracing the circuits.

You're on the right track with your suggestions. Confirm which fuse and then use these diagrams for your model year to see what's on that circuit or could come into contact with that circuit through something like the main light switch. Remove the license plate light bulbs and see if you're still blowing the fuse. Inspect for spots where wiring insulation may have frayed through and is touching chassis.

Let us know what you find.

[Firstcar]

Mike,
If Rob is right about the license plate light being on that circuit, and he probably is, I've seen those lights reconnected backwards with the ground and hot reversed cause this problem. By any chance has someone replaced the rear lplate light(s)? You might try checking the leads on one or both of those lights to see if the positive lead is accidentally connected to the ground terminal on one or both of those lights,

[Mike Bellis]

Check the brake light switch under the pedal board. Those wires can come loose and short on the pedal cluster.

[mikedsilva]

guys
great suggestions...
i will check tomorrow after work and report back.

thank you.

[thieuster]

Here's a tip.

Don't use a new fuse to test the system. Use a test system: 2 wires, 2 clamps and a small bulb (mine is a red warning light). Make sure the wiring is long enough to make the warning light visible from the point where you reconnect the wiring (e.g. als from under the bonnet). Personally, I prefer hang the lamp on a hook above my cars, so that I can see it from all angles when working on the car.

Remove the fuse and connect the contraption to the fuse terminals. Start re-attaching the connectors from 'iffy system' one by one. The moment the light comes on, you've found the culprit!

I hope that this is clear enough - I can not explain this better in English...

Menno

EDIT 1: a buzzer can be great as well when working in a spot where you cannot see the lamp...

EDIT 2: lots of info about this on YT. Try 'Test Lamp'

(IMG:http://www.914world.com/bbs2/uploads_offsite/i211.photobucket.com-18384-1426426771.1.jpg)

[Spoke]

The fuse in the number 7 spot, keeps blowing as soon as I turn the key to ignition on.

Do you have the lights in the ON position when you turn the ignition on? If the lights are off, fuse 7 shouldn't blow when you turn the key to ON.

Check the wiring at each of the lights to make sure nothing is crossed. Remove bulbs and check the sockets.

[stugray]

You can do a test like thieuster says using your DMM.

Take out the fuse that keeps blowing.With the meter set on Volts, connect the black to the car chassis, turn on the ignition, then check to see which of the two terminals have 12 volts. This is your "source" side it supplies the power.
The opposite side of where you found voltage is the "load" side.

Turn off the ignition.
Now set the meter to Ohms and IF you have the option set it to continuity or "audible".
It should beep when you connect the leads together.

Now connect the black to the car chassis again and the Red lead to the "Load" side of the fuse holder.

Read the Ohms reading on the meter and IF the short is present the meter should be sounding the audible alarm.
If you dont have the audible option, then you need to place the meter where you can see it or have someone watch it.

Now go around and wiggle the harness and connect/disconnect all of the items on that circuit.
If the audible tone goes away you have cleared the short.

[Dave_Darling]

A weird one that drove me to distraction for a long time--

The fuse panel was moving slightly in the plate that it is mounted to. When it shifted in one direction far enough, one of the hot leads would touch the mounting plate, and it would pop the fuse. This usually happened when I hit a bump in the road, but the fuse panel would shift back into place after that one brief touch. Eventually, it didn't move back into place, and I noticed that it was mis-aligned. I tightened up the loose mounting screws, and put some slit tubing along the edge of the hole in the plate to act as an insulator.

But I've also had the license plate lights hooked up backwards before, too.

--DD

[mikedsilva]

I'm certainly no master electrician either but it definitely sounds like you do have a short. Are you sure it's fuse 7? On the '71 Wiring Diagram it shows that that is only part of the license plate light circuit (through the main light switch).

Sorry, it was fuse number 8.. not 7... i was counting in the low light of the evening (that's my excuse).

So many great suggestions..
I've been googling lots and what I ended up using was a 12v bulb connected to two alligator clips.. i then attached these to the fuse terminals.

I think the theory of this, is to allow a small amount of current to flow without blowing anything major?

Anyhow, with the bulb in place and firmly lit up... i went about wiggling lots of things. I couldnt find the lic plate lights at the rear.. opened the boot and the harness was there.. with the wires taped together!
The heatshrink was still around the spade terminals under all the electrical tape, but I was so HOPING that was my short..

Installed a new fuse.. turn on ignition.... POP. gone.

My indicators just wouldnt work at all either.. they are all on the same circuit I guess..

My car is missing the wiper switch, (dash mounted knob) so I thought that maybe, a cable was earthing.. when I craned my neck underneath, I could see the switch just barely hanging there, but with no knob.
I'm not sure how these switches work.. is full anti-clockwise "off"? I used some pliers to grip the shaft, and turned it anticlockwise.. the bulb dimmed...
When I turned it back one click clockwise, the bulb went brighter... when I turned it another position clockwise (I assume this is high speed wipers) it went dim again...

So this time, I turned it all the way anti-clockwise again.. put in a fuse.. turned on the ignition and ..... nothing......the fuse didn't blow!
Now my indicators are working!
The brake lights work, but only on the left side.. i think I have a poor connection where the terminal meets the bulb...
Reverse light doesn't work either... yay.... another thing to trace.

So, from what I have described, would you say that my wiper motors are shorted/burned out?

[BeatNavy]

You have a dash mounted wiper switch (or HAD one)? I'm not familiar with that setup (is it stock on some cars)?

Brake lights: yes, clean all connections at the light thoroughly. If one side is working, it's probably just poor connections.

Reverse light: do you have a reverse light switch in the tranny and is it connected? Also, just like brake lights, clean those connections.

Right now it sounds like things have been modified / messed with, so it's hard to give you solid advice or tell you anything about your wiper motors. What you can do for the wipers is (probably with some help), test to see if your wiper motor is getting power. If you can access one of the wires (I believe green/white) at the motor see if it's getting any voltage when you turn the switch / knob (or whatever you have).

Maybe take and post a picture or two?

[Rob-O]

Sounds like the wiper motor (there is just one). I doubt it is shorted out. Instead, it's probably the shaft and arm assembly. After 40 something years, the grease inside the frame is hard and the two wiper shafts get stuck. Then you turn the switch on, the motor pulls too much juice trying to move the wipers and the fuse pops. The quick and dirty way is to spray WD-40 or some other lubricant down the shafts from the cowl areA. The correct way is to pull the tank, the fresh air box (which will probably need attention too), remove the wiper assembly/motor, disassemble, lubricate, reassemble and reinstall.

Search the forum, this has been discussed many times. There may even be a classic forum thread with pictures.

[boxstr]

Pull the wires out of the reverse light switch on the transmission, and then check your 7 fuse. I had this same problem, found a bad reverse light switch.
Craig at CAMP

[gopack]

Sounds like the wiper motor (there is just one). I doubt it is shorted out. Instead, it's probably the shaft and arm assembly. After 40 something years, the grease inside the frame is hard and the two wiper shafts get stuck. Then you turn the switch on, the motor pulls too much juice trying to move the wipers and the fuse pops. The quick and dirty way is to spray WD-40 or some other lubricant down the shafts from the cowl areA. The correct way is to pull the tank, the fresh air box (which will probably need attention too), remove the wiper assembly/motor, disassemble, lubricate, reassemble and reinstall.

Search the forum, this has been discussed many times. There may even be a classic forum thread with pictures.

FWIW
Just wanted to point out: WD-40 is not a lubricant! more of a penetrant, and even then actually more of a water displacement formula. use it to free things up, but use spray grease or a drop of lube of choice on the wiper mechanism joints.

[mikedsilva]

update...
I got the wipers to start working.. not sure how, but it occurred after I had the battery on charge and whilst it was still connected to the charger.
The wipers started to move ever so slowly.... when I pulled them off the screen, they seemed to work fine in mid air. Low speed, high speed and the park function.

The next night I came down to have a play with the car... the fuse blew again.

I couldn't understand why... I thought I had it all sussed.

A friend came over, and had a look at some wiring and we could see that there were new terminals plugged into the harness where the wiper motor was....

So I proceeded to remove the tank...

Once out, I could easily see the wiring... here is a photo...
(IMG:http://www.914world.com/bbs2/uploads_offsite/i1260.photobucket.com-18462-1427659080.1.jpg)


And here is one of the wiper motor....
(IMG:http://www.914world.com/bbs2/uploads_offsite/i1260.photobucket.com-18462-1427659080.2.jpg)

I'm no expert but I did have the haynes... there was one spare wire hanging which I was certain should have been attached to the ground tab on the motor.. also, my motor doesn't have the white block of terminals like most research shows... has a harness that comes from the motor itself.. I am guessing this is a replacement motor.

[mikedsilva]

I ended up removing the wiper motor.
I marked all wires with tape so I could plug it back in as it came out.

On the bench, I connected power to the various wires, and was able to ascertain which wires gave, low speed, high speed, park function.

The wiper motor itself seems to work fine on the bench... so I guess that eliminates the motor as being the problem.
I haven't been able to confirm which wires that come from the switch, are supposed to be for high, low and park.. but I was able to find that the brown wire was supposed to be connected to the chassis of the motor.
I plugged the motor back into the car, and connected the brown from the switch, to the ground tab on the motor. The "loose" green wire with stripe was then plugged into the motors now unused connector; now everything seems to work fine.

Problem is that when the wipers are on the screen, they do not have enough power to wipe... granted, the screen is dry and the blades are old...

I'll be confirming with a friend this week, if I have indeed connected everything correctly..

[GaroldShaffer]

I ended up removing the wiper motor.
I marked all wires with tape so I could plug it back in as it came out.

On the bench, I connected power to the various wires, and was able to ascertain which wires gave, low speed, high speed, park function.

The wiper motor itself seems to work fine on the bench... so I guess that eliminates the motor as being the problem.
I haven't been able to confirm which wires that come from the switch, are supposed to be for high, low and park.. but I was able to find that the brown wire was supposed to be connected to the chassis of the motor.
I plugged the motor back into the car, and connected the brown from the switch, to the ground tab on the motor. The "loose" green wire with stripe was then plugged into the motors now unused connector; now everything seems to work fine.

Problem is that when the wipers are on the screen, they do not have enough power to wipe... granted, the screen is dry and the blades are old...

I'll be confirming with a friend this week, if I have indeed connected everything correctly..

If you haven't already pull the wiper rack out clean & lube all the joints you can. I had the same problem with my 70. I had to pull the wiper rack and clean it up and lube every joint. Since then they have worked just fine and that was 7yrs ago. Once a year I pull the wiper arms off and the nuts & washers then drop a few drops of oil in there and then put back together.